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#10 Deal with Nested Array in Documents in MongoDB

What is Nested Array in Documents?

In MongoDB, documents can contain arrays as values, which can, in turn, contain other arrays or documents.

  • In this document, the field skills is an array, containing several string elements.
  • The field contacts is a nested array, containing several array elements.
[
  {
    _id: ObjectId('66053f848ccb6407b4ba21c6'),
    name: 'Michael Johnson',
    age: 35,
    working_experience: 8,
    department: 'Finance',
    salary: 70000,
    skills: [ 'Accounting', 'Financial Analysis', 'Excel' ],
    contacts: [
      { type: 'address', value: '123 Street' },
      { type: 'Email', value: 'abc@xyz.com' }
    ]
  }
]
nested array screenshot
nested array screenshot

Query Nest Array

You can query documents based on fields within nested arrays using dot notation.

db.personnel.find({"contacts.type": "Email"})

Update Nest Arrays

Updating Elements: Use the positional $set operator and $ to update specific elements within a nested array.

For example, I want to change the address 123 Street to 789 Street.

> db.personnel.update({"_id":ObjectId("66053f848ccb6407b4ba21c6"),
                       "contacts.type":"address" }, 
                      { $set: { "contacts.$.value": "789 Street" } }  )

#let's check the result
> db.personnel.find({"name":"Michael Johnson"}) 
[
  {
    _id: ObjectId('66053f848ccb6407b4ba21c6'),
    name: 'Michael Johnson',
    age: 35,
    working_experience: 8,
    department: 'Finance',
    salary: 70000,
    skills: [ 'Accounting', 'Financial Analysis', 'Excel' ],
    contacts: [
      { type: 'address', value: '789 Street' },
      { type: 'Email', value: 'abc@xyz.com' }
    ]
  }
]

Adding Elements: You can use $push to add elements to a nested array.

For example, I want to add a new address called 456 Street to the employee Michael Johnson.

> db.personnel.update({ "_id": ObjectId("66053f848ccb6407b4ba21c6")}, 
                      { $push: { "contacts": 
                                  { "type": "address", "value": "456 Street" } } } )


#let's check the result
> db.personnel.find({"name":"Michael Johnson"}) 
[
  {
    _id: ObjectId('66053f848ccb6407b4ba21c6'),
    name: 'Michael Johnson',
    age: 35,
    working_experience: 8,
    department: 'Finance',
    salary: 70000,
    skills: [ 'Accounting', 'Financial Analysis', 'Excel' ],
    contacts: [
      { type: 'address', value: '789 Street' },
      { type: 'Email', value: 'abc@xyz.com' },
      { type: 'address', value: '456 Street' }
    ]
  }
]

Removing Elements: You can use $pull to remove elements matching a specific condition from a nested array.

For example, I want to remove all the address info from this document.

> db.personnel.update({ "_id": ObjectId('66053f848ccb6407b4ba21c6')},
                      {$pull:{"contacts":{"type":"address"}}})

# let's check the result
> db.personnel.find({"name":"Michael Johnson"}) 
[
  {
    _id: ObjectId('66053f848ccb6407b4ba21c6'),
    name: 'Michael Johnson',
    age: 35,
    working_experience: 8,
    department: 'Finance',
    salary: 70000,
    skills: [ 'Accounting', 'Financial Analysis', 'Excel' ],
    contacts: [ { type: 'Email', value: 'abc@xyz.com' } ]
  }
]
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